1. Field of the Invention
The present invention relates to an image information transmission apparatus for transmitting image data as a block code.
2. Related Background Art
A typical conventional encoding scheme for reducing the mean number of bits per sampling frequency or per pixel is known as a method of reducing a transmission band with of a television signal. In the scheme for reducing the mean number of bits per sampling frequency, the image data are interlaced into a half by sampling, and sampling points and a flag, representing positions of sampling points used for interpolation (i.e., a flag representing use of data of upper and lower or right and left sub-sampling points of the interpolation point) are transmitted.
A typical example of the scheme for reducing the mean number of bits per pixel is a block encoding scheme for segmenting a screen of one field into small blocks and encoding is performed in units of blocks (e.g., U.S. Pat. No. 4,703,352). For example, the difference between minimum and maximum values of a block of interest is either linearly or nonlinearly quantized An index representing a quantization level to which each pixel belongs is transmitted, and the minimum and maximum values are transmitted as scale components.
In this block encoding scheme, encoding is performed on the basis of the dynamic range of intrablock pixel values. However, if an extreme contrast difference is present within a block, or a boundary is included in a block, so that a distribution of pixel values is greatly different from that of an assumed state, large distortion occurs in a decoded signal.